Regulators of denitrification in an organic riparian soil

• Published in: Soil biology & biochemistry Vol. 25; no. 7; pp. 925 - 933
• Main Authors: Schipper, L.A., Cooper, A.B., Harfoot, C.G., Dyck, W.J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1993; New York, NY Elsevier Science
• Subjects: Agronomy. Soil science and plant productions; biological activity in soil; Biological and medical sciences; denitrification; discharge; Fundamental and applied biological sciences. Psychology; groundwater flow; landscapes; nitrate renovation; nitrates; organic soils; riparian zone; Soil and water pollution; Soil science; water pollution; water quality; watershed hydrology; New Zealand; Oceania; Microbial activity; Forest zone; Lysimetry; Organic soil; Nitrates; Waste water; Soils; Regulation(control); Nitrogen cycle; Volcanic soils; Enzymatic activity; Water quality; Denitrification; Water pollution; Saturated soil; Nitrogen protoxide; Inceptisols; Drainage water; Riparian forest; Ground water
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(93)90095-S

We investigated microbial denitrification in an organic riparian zone and identified factors which regulated its rate. The riparian zone received nitrate from incoming groundwater draining an upslope forest which was spray irrigated with treated effluent. Soil cores were taken from the riparian zone and the following variables were measured: KCl-extracted nitrate, water soluble carbon concentration, organic matter content, moisture content, denitrifying enzyme activity, on-site denitrification rates and natural N 2O production. Five sampling surveys were made at a range of field temperatures (12–21°C). The riparian soil was continually water-saturated and contained an average organic matter content of 26%. Nitrate concentration in groundwater entering the upslope edge of the riparian zone was generally greater than 5 mg N l −1. In combination, these factors resulted in an ideal environment for denitrification. Mean and median denitrification rates were found to be 1.12 and 0.95g N m −2 day −1; while mean and median N 2O production rates were 73 and 84 mg N m −2 day −1 These rates were 1–3 orders of magnitude greater than those reported in previous studies of upland soils. Up to 77% of the variation in on-site denitrification rate could be explained by nitrate concentration and denitrifying enzyme activity. Temperature may also have regulated the rate of denitrification; however, insufficient observations at different temperatures were made to fully establish a temperature effect. N 2O production was found to be most highly correlated to on-site denitrification rate. Rates of denitrifying enzyme activity were also greater than those generally found in upland soils, the mean and median rates were 810 and 740 ng N g −1 h −1